Moisture sensors are used in agricultural harvesting equipment in order to obtain a measure of the moisture of the harvested product. Some current moisture sensors sense moisture by measuring the dielectric permittivity of the harvested product at one or more frequencies and then applying a calibration function in order to estimate the moisture, from the measured permittivity. Some such moisture sensors use a capacitive structure in which the harvested material forms the dielectric medium in the capacitive structure.
There are a variety of different types of moisture sensors, which have different geometries. One geometry involves the capacitive structure being formed as a parallel plate structure in which the material being measured passes between the plates of the capacitive structure, and forms the dielectric medium. One of the two plates is driven with an excitation voltage and the other plate senses current induced by an electric field passing through the capacitive structure. This type of structure works well for many materials, such as grains.
Some moisture sensors are also planar structures. The planar structures have a drive electrode to which an excitation voltage is applied, and the current passing through the drive electrode is also measured. The drive electrode sets up a fringing electric field that passes from it, out through the material being measured, and back to various grounded conductive surfaces in the same plane. The drive voltage and resulting current are measured and used to compute the permittivity of the measured material. These types of sensors can work better with soft, compressible material (such as hay, cotton and forage) that do not flow easily through a parallel plate structure.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.